1. Field of the Invention
The present invention relates to an apparatus and method for detecting an object such as a pedestrian from an image obtained via an image pick-up means such as a camera, a vehicle mounted with the apparatus, and a program for causing a computer to carry out the processing of the apparatus.
2. Description of the Related Art
Recently, there is known a technique of detecting an object such as a pedestrian existing around a vehicle from an image picked up by an image pick-up means such as a CCD camera mounted on the vehicle to determine an object whose contact with the vehicle should be avoided and providing such information to the driver of the vehicle (see, for example, Japanese Patent Application Laid-Open No. 2001-006096 (Patent Document 1)).
In the vehicle surroundings monitoring apparatus disclosed in Patent Document 1, the images of the surroundings of the vehicle obtained by two infrared cameras are subjected to binarization processing to extract an object, and a relative position or relative speed of the object and the vehicle is detected, to thereby determine the possibility of contact of the object with the vehicle as well as the type of the object. The apparatus of Patent Document 1 determines the type of the object (pedestrian, other vehicle, man-made structure or the like) in the case where there is an object in an approach determination area in front of the vehicle (which area is determined according to the relative speed of the object to the vehicle, the width of the vehicle, or the like). In determination of the type of the object, a characteristic of the shape pattern of the image portion of the object in the image picked up at a prescribed time is used. If it is determined that the object is a pedestrian, the object is determined to be an object whose contact with the vehicle should be avoided.
In the case of a moving object, such as a pedestrian, animal or the like, the shape pattern of its image portion would change in various manners over time, making it difficult to expect all the shape patterns in advance. Thus, in the case of determining the type of the object using the shape pattern of the image portion, it will be difficult to detect a pedestrian or the like if its image portion is in an unexpected shape pattern.
Generally, the movements of the pedestrian, animal and the like each have a prescribed rhythm. Taking this into consideration, there is proposed an apparatus which determines the type of the object by detecting the pattern of movement of the object through processing of time series images (see, for example, Japanese Patent Application Laid-Open No. 7-050825 (Patent Document 2)).
In the human being and animal monitoring system disclosed in Patent Document 2, an infrared image picked up by an infrared camera is subjected to binarization processing to extract an image portion of the object (object image). Then, periodicity in change of areas of the portions corresponding to left and right legs within the object image is examined to determine whether the object is a human being or an animal.
For example in the case of extracting the object image through binarization of an infrared image, however, the area may not be obtained in a stable manner due to the influence of the surrounding environment. Specifically, in the case of binarization using a prescribed threshold value, a part of the leg may not be extracted as an area of high luminance, depending on the outdoor air temperature. In such a case, the determination of the type of the object using the change amount of the area of the leg portion alone, as in Patent Document 2, may lead to an erroneous determination.